My fingers don't extend like in either picture (looking like they are going to snap) very well, so I never crimp like that.
I tend to use my thumb as much as possible though, either on another part of the hold or turning the hold into a sort of pinch style affair.
In the past on some really gash holds (undercut sidepull of out of my boots), I have tried to throw my thumb well over my index and middle finger in a sort of bizarre claw shape. It doesn't really work as well as half crimping though.
